As one of wireless communication systems, there is a wireless communication system including a relay station (repeater).
By relaying a wireless signal between a wireless base station and a wireless terminal by a relay station, it is possible to increase a wireless transmission distance or to extend a communication service area.
For example, when the relay station is installed at the edge of the communication service area of the wireless base station, since the relay station is operable to amplify and reradiate a radio wave from the wireless base station, it is possible to increase the wireless transmission distance or to extend the communication service area.
Further, in the wireless communication system, there are cases in which a transmission power control (TPC) is performed on wireless terminals in order to reduce interference between wireless signals and suppress battery consumption of the wireless terminal to thereby satisfy both maintaining of a communication quality and transmission power saving.
As one of transmission power control schemes, for example, there is a closed loop transmission power control (closed loop TPC) scheme.
In the closed loop transmission power control scheme, for example, a wireless base station controls a transmission power of a wireless terminal based on a signal to interference power ratio (SIR) related to a wireless signal received from the wireless terminal. Specifically, for example, the wireless base station controls the transmission power of the wireless terminal by transmitting a control command (TPC bit) to instruct an increase or decrease in a transmission power so that an SIR on the wireless signal received from the wireless terminal gets close to a target SIR to the wireless terminal.
Note that, as an existing technique related to a transmission power control, techniques of Patent Documents 1 to 3 listed below have been known.
For example, Patent Document 1 discloses a method in which a wireless base station switches multi-antenna communication schemes including a transmission power control method according to an estimation of a delay time of a feedback signal from a mobile station.
Further, Patent Document 2 discloses a method in which a wireless base station compensates for an error in a transmission power setting based on an SINR of user equipment (UE).
Furthermore, Patent Document 3 discloses a method in which a base station apparatus switches power control schemes based on a comparison between information related to a moving speed of a terminal and a predetermined threshold value.